The present invention therefore applies to the rolling of an aircraft on the ground, in particular an airplane, civil or military, for transporting passengers or merchandise (freight), or else a drone. It relates more particularly to an automatic lateral guidance making it possible to slave, in relation to the lateral axis and along a given trajectory, an aircraft rolling on the ground.
Within the framework of the present invention, the following meanings are implied:                “rolling on the ground” implies any type of possible rolling of an aircraft, such as rolling on a landing runway in the course of the landing and takeoff phases, or rolling on trafficways or on maneuvering areas, in particular; and        “automatic lateral guidance” implies the action of a system forming an integral part of the aircraft and capable of ensuring, partially or totally, that is to say without aid or with the partial aid of a (human) operator, the driving of an aircraft on the ground in relation to the lateral axis.        
Currently, the pilot controls the lateral movements of the aircraft on the ground with the aid of manual piloting facilities (for example a steering wheel allowing the orientation of the wheel of the front landing gear, a lever for controlling the thrust of the engines, brake pedals, a direction rudder bar), along a ground trajectory. These facilities make it possible to control actuators of the aircraft capable of influencing the lateral movements of the aircraft, in particular by way of the orientation of the wheel of the front landing gear (and optionally of the orientation of the rear gear) and of the rudder of the fin, as well as of the asymmetric use of the engines and brakes.
The term “ground trajectory” designates the pathway followed by the aircraft on an airport domain such as an airport or aerodrome, including in particular the takeoff and landing runways, the trafficways or taxiways, the turn-around areas, the waiting zones, the stop bars, the stopping positions (stand), the maneuvering areas, and the parking areas.
The ground trajectory is generally provided to the pilot by an air traffic controller or ground controller, for example by way of radiocommunication means or some other standard means such as a digital data transmission link, but it can also, in certain cases, be chosen freely by the pilot.
The trajectory is defined in the form of a succession of elements of the airport domain, and indicates a path making it possible to attain, from one point or region of the airport domain, another point or region of this domain.
Any portion of the domain, whether or not designated by a name, and identified as a distinct and delimited part of the domain, is called an element of the airport domain. An element may optionally overlap one or more others. The takeoff and landing runways, the trafficways or taxiways, the turn-around areas, the waiting zones, the stop bars, the stopping positions (stand), the maneuvering areas and the parking areas are in particular designated as elements.
Knowing the ground trajectory to be followed, the pilot acts on the piloting facilities, so as to control the movements of the aircraft on the ground (the longitudinal speed and the lateral displacements of the aircraft). He does so also in order to follow the trajectory in such a way that all the parts of the aircraft in contact with the ground (the wheels of the front and rear gear) remain permanently on the pavement designed for aircraft rolling. For most airports accommodating civil or military transport airplanes, the term “ground” implies the parts covered with tarmac and designed for this purpose. The pilot's objective is therefore to follow a trajectory so that none of the parts of the aircraft in contact with the ground lies, at a given moment, on a portion of the airport domain that is not designed for the rolling of the aircraft, in particular portions covered with grass, earth or sand, or portions designed solely for the rolling of lighter vehicles (cars, trucks).
The pilot may optionally be helped by the aid of a map of the airport (in paper or computer format) to carry out the manual guidance of the aircraft along the trajectory, while monitoring the exterior environment thereof.
Manual piloting of an aircraft on the ground nevertheless constitutes a significant workload for the pilot. The latter must in fact follow the scheduled trajectory by controlling the rotation of the aircraft in relation to the yaw axis (with the aid of the steering wheel and rudder bar), while taking care not to depart from the pavement designed for the rolling of the aircraft, and while simultaneously monitoring the exterior environment, and in particular:                the movements of the other vehicles traveling around the airport domain, in particular aircraft currently rolling on the ground, taking off or landing, cars, trucks, etc.; and        the obstacles present around the aircraft and liable to cause a collision with the latter, in particular buildings, gangways, antennas, indication and signaling panels, and other vehicles on the ground, stationary or otherwise (aircraft, cars, trucks, mobile gangways).        
This significant workload may, consequently, influence the pilot's vigilance, and lead, in particular, to the following of an unscheduled trajectory, departures from the pavement designed for the rolling of the aircraft, and collisions with other vehicles or obstacles that may lead to significant damage to equipment and humans.
When conditions exist that are detrimental to the visibility (for the pilot) of the exterior environment, in particular at night or during unfavorable meteorological conditions (in particular fog, snow, rain, storms, etc.), the pilot may be dependent on exterior aid for piloting the aircraft, for example the aid of a vehicle to be followed which makes it possible to guide the aircraft visually along the trajectory by traveling ahead of it at low speed. Dependence on exterior aid such as this is often penalizing for airlines, since the low-speed movement of the aircraft may induce delays in the scheduled timetables. In certain cases, in particular in the event of extreme meteorological conditions, the airport traffic may even remain totally paralyzed if the exterior aid turns out to be ineffective, thus leading to delays and significant costs for the airlines.
Additionally, the driving of aircraft of significant length can be difficult to achieve, in particular during turns, because of the significant wheelbase between the front and rear gear. Under these conditions, it is, in fact, more difficult to drive the aircraft so that all the parts in contact with the ground remain on the pavement designed for the rolling of the aircraft, thereby requiring the use of additional pilot aids, for example the employing of exterior cameras allowing the pilot to verify that the wheels of the front gear do not depart from the pavement (the case of transport airplanes of the A 380 and A340-600 types).
Furthermore, the manual guidance of the aircraft does not offer any guarantee in terms of accuracy of trajectory tracking. In particular, it does not make it possible to quantify the gaps between the wheels of the front and rear gear and the edges of the pavement, or the gaps between a given point of the aircraft and the paint on the ground or the trajectory to be followed, or any other reference that may serve as support for lateral guidance.